As the method for giving excellent mono-color or multi-color images simply and at high speed the ink jet system, the heat transfer system, etc. have been developed instead of the general letter printing method or the printing method of the prior art. Among them, the so-called heat transfer system is the most excellent by use of a heat migratable dye as the method capable of giving a multi-color image comparable to those of color photography and having excellent continuous gradation characteristics.
For the heat transfer sheet to be used in the above heat transfer system, there has been generally employed one obtained by forming a dye layer containing a heat migratable dye on one surface of a substrate film such as polyester film, etc., while on the other hand providing a heat resistant layer on the other surface of the substrate film for prevention of stickiness of the thermal head.
By superposing the dye layer surface of such a heat transfer sheet onto the image-receiving material having an image-receiving layer comprising a polyester resin, etc., and effecting heating imagewise by a thermal head on the back surface of the heat transfer sheet, the dye in the dye layer is migrated onto the image-receiving material to form the desired image.
In the heat transfer system as described above, no satisfactory transferred image can be formed on an image-receiving material having basically no dyeability to dyes, for example, papers such as plain paper, pure paper, etc. moldings comprising thermosetting resins, nondyeable thermoplastic resin films or moldings, metal plates, glass plates, porcelain and earthenware, etc.
Also, when an image is formed with a mass of fine dots, if there is unevenness on the surface of the image-receiving material, "drop-out" (pinhole) will be undesirably generated.
Accordingly, it is generally practiced to prepare an image-receiving sheet for exclusive use with "attachment" of the dye on the surface being improved to give unevenness on the smaller surface, by previously coating the image-receiving substrate such as paper, plastic, etc. However, image-receiving substrates previously prepared cannot be suitable for all uses, and also the preparation of various substrates coated with resins for specific uses involves many demerits in aspects of steps, materials, storage, transport, etc., and there is the drawback that the product cost may be considerably increased.
Particularly, when it is desired to form an image on a part of the substrate, other working may be sometimes applied to the residual portion, whereby coating of a resin on the entire surface is not only superfluous, but even a trouble may be caused to occur.
As an example, when the face picture of a possessor is to be formed on a card for identification, the face may be sufficiently present in the region with a size of about 2 to 3 cm square, and when other working such as printing, signature or others is to be applied at other portions, the resin must be coated only at the determined portions, and since the region to be coated differs depending on the card for identification, it cannot be used interchangeably for different cards for identification.